Chance brings us another Grade 1 singer today, an owl. Actually two owls, a pair duetting. This is a new wrinkle, the first time we've had a pair singing together. We might pause to ask here "what is a duet?" in the bird world. Is it two birds jointly declaring the ownership of their territory to neighbors and would-be intruders? There are species in which male and female both contribute indistinguishably to each song. I bet those qualify as joint defense songs. In other species, the male and female are talking to each other, sociably. I think that's what we have here. Let's take a listen.
Having read Don Kroodsma's account of the Barred Owl on pages 336-346 of The Singing Life of Birds, I'm ready to tell you what we're hearing in the cut above. These birds are duetting at dawn, so we have a full program of daybird singing to deal with. Focus on the lowest 2 kHz of the moving sonogram and allow these birds to take you back to the swamp. The most rambunctious part of their duet is the first 21 seconds. One bird is caterwauling, the other gives at least one who-cooks-for-you call and a variety of other sounds. The maniacal cackling is what we call caterwauling, and it is typically a male contribution, according to Kroodsma. After a pause of 15 seconds, the birds engage in a minute and a half of antiophonal legato calling. The female, the one with the higher voice, seems to be leading. The male follows, often overlapping her, but sometimes waiting for her to finish. In owls, females are larger but the males have the lower voices. The default is for larger-bodied birds to produce lower-pitched sounds, so the pitch disparity cries out for an explanation. Perhaps the lower pitch of males is an unselected side effect of their higher testosterone levels, perhaps it is the result of natural selection for low pitch, or maybe something else. Regardless, it is also seen in the tiny Flammulated Owl, which I hope to demonstrate sometime soon.
In addition to pitch, we have another clue to the sex of hooting Barred Owls. The last note of the legato call, which is also the last note of who-cooks-for-you, is drawn out into you-all in females. Knowing this, you can easily tell the male from the female above. Listen again and give it a try.